1. Field of the Invention
The present invention relates to a facsimile communication system and a communication apparatus.
The present invention also relates to a data communication apparatus having ability of data communication by a full duplex communication mode.
2. Related Background Art
In a prior art facsimile communication system of this type, a communication system by a half duplex communication mode defined by T.30 of the ITU-T T-series Recommendation as shown in FIG. 9 has been commonly adapted.
However, in the prior art system, in the communication of a communication protocol of other than image information by V.21, a synchronization signal of approximately one second is added in front of data in each protocol signal in order to synchronize the data reception at both sending and receiving stations. Thus, in order to send data of 0.1 second length, for example, a signal of 1.1 second must be sent and an extra communication time is needed by the synchronization signal.
A facsimile apparatus has been known as an apparatus of this type. When full duplex communication is to be conducted through a public line, it is necessary to disable a function of an echo suppressor (or echo canceler) provided in a public network. The function of the echo suppressor in the public network is disabled by sending a signal of 2100 Hz of a predetermined duration (500 msec to 1 sec) to the line and enabled by the interruption of the signal on the line for 100 msec or longer.
In a prior art full duplex communication facsimile apparatus, a protocol signal is communicated in the half duplex mode and an image signal is communicated in the full duplex mode. Since the interruption of signal for 100 msec or longer may occur in the communication of the protocol signal in the half duplex mode, a signal of 2100 Hz is sent for a predetermined time interval in order to disable the echo suppressor immediately before each communication of the image signal and then the image signal is communicated in the full duplex mode.
However, the signal of 2100 Hz to disable the echo suppressor need be sent for 500 msec to 1 sec. When the signal of 2100 Hz is sent for each communication of one page of image signal, the communication time is increased by the signal of 2100 Hz if a plurality of page of image signals are sent.
As the modem technology is advanced in recent years, the transmission speed has been increased. However, when the disable (disenable) signal for the echo suppressor is sent for each communication of one page of image signal, the decrease of the communication time is not efficiently attained.
It is an object of the present invention to provide a data communication apparatus which can shorten the communication time.
It is another object of the present invention to provide a facsimile communication system and a communication apparatus which can reduce a loss time due to the synchronization of both sending and receiving stations and shorten the communication time.